1. Field of the Invention
The present invention relates to compositions that suppress after curing color reversion of photocuring materials which sufficiently cure to the interior of the compositions, even when the compositions contain pigments and coloring dyes with high masking ability, or have a high thickness or contain poor light transmitting materials, as well as to a color reversion-preventing method.
2. Description of the Related Art
Photopolymerization has been conventionally employed for a wide range of multifaceted uses, including curing of coatings, printing resin relief-printing, printed board construction, resist and photo masking, black-and-white and color transfer coloring sheets and coloring sheet preparation, etc., and the recent focus on environmental issues, energy conservation and labor-saving means to counter increasing labor costs has stimulated active development with an emphasis on polymerization at normal temperature, rapid drying and the ability to be used without a solvent, which are features of photopolymerization. Photocuring which is carried out by cationic polymerization or radical polymerization by irradiation with ultraviolet light of 200-400 nm generally allows rapid curing of polymerizable monomers and oligomers. However, the poor penetration of ultraviolet light has been a problem with colored coatings containing pigments or dyes with strong masking powers, and photocuring has therefore been associated with the disadvantage of a very poor curability of coating interiors. In order to overcome this problem there have been proposed, in Japanese Unexamined Patent Publication No. 4-80204, No. 5-59110 and No. 10-81838, photopolymerization initiators made from cationic dyes, with absorption in the visible light range, and quaternary organo borates. These photopolymerization initiators initiate radical polymerization upon irradiation with light, and allow sufficient curing to the coating interiors even when high-masking pigments are present. Nevertheless, although the color of the cationic dye first disappears completely during the photopolymerization, the color reappears after continued use, thus disadvantageously impairing the color of the cured product. For this reason, these initiators are totally unusable for applications in which the colors of cured products, such as paints and inks, are important.